Many medical devices for helping people who have lost their hearing by nature or in the course of their lifetime are being developed. In particular, a cochlear implant apparatus that helps people having live auditory nerves to sense sound by stimulating the auditory nerves with electricity has been recognized as being the most efficient device of tributary nerve devices that have now been developed so far. The transplant operations of such cochlear implant apparatuses are increased every year.
The conventional cochlear implant apparatus may be divided into a part outside the body and a part inside the body depending on its installation place. The conventional cochlear implant apparatus is configured to include an external device configured to receive sound outside the human body and an internal device inserted into the human body and configured to stimulate the auditory nerves. The part outside the body that is installed outside the body includes a microphone (or a transmitter), a sound processor (or a language synthesizer), and an antenna for transmission (or a sender). In this case, the microphone and the antenna for transmission are also called a headset. The part inside the body that is implanted into the body includes an receptor/stimulator (or a receiver) and an electrode.
Accordingly, in the conventional cochlear implant apparatus, a sound signal transferred by the microphone attached outside the human body is subject to the amplification of an external sound processor and the filtering of a filter without passing through an ark shell or the auditory ossicles. Physical vibration obtained by such processes is converted into an electrical signal and is transferred to the auditory ganglion through the electrode implanted within the cochlear implant apparatus. To this end, the conventional cochlear implant apparatus requires the transmitter configured to receive sound outside the body and an external device that consumes a lot of power in order to analyze and process the sound signal and to convert the processed signal into an electrical signal.
Accordingly, the conventional cochlear implant apparatus is problematic in that a long time is taken for a user to be accustomed to the cochlear implant apparatus as part of his body because separate equipment must be always attached outside the human body and a third party may become aware of the cochlear implant apparatus.
Furthermore, pieces of sound present in the natural world have a severe pressure deviation. A difference between small sound and great sound is about 180 dB, that is, a difference corresponding to trillions. A microphone capable of linearly processing such sound pressure is now not present. A device capable of processing such sound process most efficiently may be said to be a cochlea within the body.
In this case, the cochlea of the human body includes an outer hair cell and an inner hair cell. The outer hair cell becomes long in a low frequency and becomes short in a high frequency. The cochlea can recognize sounds of various magnitudes according to a pressure deviation through a change in the length of the hair cells. That is, the outer hair cell of the cochlea changes its length depending on sound pressure so that an excessively great sound is recognized as being small and an excessively small sound is recognized as being great.
The conventional cochlear technology, however, does not implement a mechanism, such as the outer hair cell of the cochlea, and is problematic in that sound of various magnitudes are not classified and recognized because a change according to a pressure deviation between the sounds is not detected.
For this reason, recently, there is a need for a technology capable of dividing sounds of various magnitudes according to a pressure deviation and controlling the sensitivity of a sound by simulating a mechanism, such as the outer hair cell of the cochlea.